"His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure." - Neil deGrasse Tyson, director of New York's Hayden Planetarium, on Twitter .

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"Stephen Hawking will be remembered for his incredible contributions to science - making complex theories and concepts more accessible to the masses. He'll also be remembered for his spirit and unbounded pursuit to gain a complete understanding of the universe, despite the obstacles he faced." - Satya Nadella, Microsoft CEO, on LinkedIn .

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"Professor Stephen Hawking was a brilliant and extraordinary mind - one of the great scientists of his generation. His courage, humour and determination to get the most from life was an inspiration. His legacy will not be forgotten." - British Prime Minister Theresa May, on Twitter .

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"His contributions to science will be used as long as there are scientists, and there are many more scientists because of him. He spoke about the value and fragility of human life and civilisation and greatly enhanced both." - University of Manchester physicist Brian Cox, on Twitter .

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"I feel lucky to have known Stephen Hawking. His work is an inspiring reminder of what human minds are capable of." - Bill Gates, Microsoft co-founder, on Twitter .

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"I join the global community in mourning the loss of the greatest physicist of our era. #StephenHawking is free from the physical constraints of this earthly condition we all exist in and he is soaring above us now marveling at it all." - actress Mayim Bialik, who appeared with Hawking on the U.S. television show "The Big Bang Theory," on Twitter .

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"We have lost a truly beautiful mind, an astonishing scientist and the funniest man I have ever had the pleasure to meet. My love and thoughts are with his extraordinary family." - actor Eddie Redmayne, who played Hawking in the 2014 film "The Theory Of Everything."

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"When a brilliant scientific mind like Stephen Hawking also happens to be a great popularizer of science, it's a gift to the world. Here's hoping there are more like him waiting to be known." - Seth MacFarlane, executive producer of the 2014 TV series "Cosmos: A Spacetime Odyssey," on Twitter .

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"Remembering Stephen Hawking makes me want to work harder on both my research AND my public engagement. I want to understand the Universe, and I want to share it with the world." - Dr. Katherine J. Mack, North Carolina State University astrophysicist, on Twitter .

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"He was a true genius who had a great admiration of and connection to the public. ... He simplified and explained, but without gimmicks. His assumption that people are curious about the universe and black holes was true. He inspired us all to wonder." - Katherine Mathieson, chief executive of the British Science Association.

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"He inspired generations to look beyond our own blue planet and expand our understanding of the universe. His personality and genius will be sorely missed." - British astronaut Tim Peake on Twitter .

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"Along with groundbreaking and inspiring work came another attribute that made Stephen a hero not just to younger generations, but also to his peers. A longtime friend to NASA, Stephen was a passionate communicator who wanted to share the excitement of discovery with all." - acting NASA Administrator Robert Lightfoot.

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"His name will live in the annals of science. Millions have had their cosmic horizons widened by his best-selling books. And even more around the world have been inspired by a unique example of achievement against all the odds - a manifestation of amazing will-power and determination." - Martin Rees, British astronomer royal.